The Apple II (also known as the Apple ][) was a home computer released in 1977, with many hardware models and clones along the years. The Apple II became one of the first widely successful home computers in the world, rivaled by the likes of the Commodore 64.
Applewin is a very stable emulator with internal pausing and screenshot features. Newer releases of the program do not have the option to set the display to "Color (TV Emulation)" which is necessary to achieve pixel perfect video. Version 220.127.116.11 is recommended, and easy to find with a proper search.